Begin by selecting the World Cities layer by clicking on its name in the Layer Control Panel. You can tell when the Layer is selected because its Control Panel will appear with an orange border and a background color different from the other layers. Once you have selected the World Cities layer, click on the Data Table button, as shown in Figure11 below.
Let's explore the relationship between population and geography in the United States. To do this, we will need to add some additional layers. We will also learn to use Analyze Mode to create selections of U.S. Cities based on geographic features.
First, zoom in on the continental United States using the Zoom In tool to drag a box around the continental United States, as demonstrated earlier.
Next, return to Construct mode. In the Data Library, change the Library menu to the "United States" data library. Then, drag the "U.S. Cities" layer from the to the top of the Layer List, as shown in Figure15 below. (Be sure to add "U.S. Cities" above the "Countries" and "World Cities" layers; this will make it appear on top of those layers).
Figure 15. Adding the "U.S.Cities" layer to the top of the Layer List
Now that you have added "U.S. Cities" to the map, return to Visualize mode. Next, hide the "World Cities" layer by clicking on the check box in the upper-left corner of the Countries layer's Layer Control Panel, as demonstrated earlier.
Now, you are ready to analyze the "U.S. Cities" layer. Our first step will be to select all U.S. cities with populations of one million or greater. To do this, click on the tab for Analyze mode at the top of the My World Window, as shown below in Figure16.
Figure 16. Analyze Mode
In Analyze mode, you will see a list of analysis choices on the left. Go to the Select... folder and click on By Value, as shown below in Figure17. This feature allows you to query records in a given layer based on the value of a specific field. To select cities with populations over one million, follow the guided text and use the pulldown menus to construct your desired selection. For example:
Figure 17. Selecting data by value
You can name the result, or click "OK" and My World will suggest a name for you.
After performing the calculation, My World will return you to the map, having highlighted your selected cities in yellow. It may be hard to notice with all the other cities visible, so you can Hide Unselected cities using the pulldown menu in the U.S. Cities Layer Control Panel, as demonstrated earlier.
To identify the cities, choose the Get Information Tool from the toolbar. When you click it, My World will ask you which layer you want to identify; e.g., "U.S. Cities". Once you have done this, click on any city. This will give you a table containing all available data for each city. The information changes as you click on different cities. When you are finished, you can close the table.
What do you notice about the locations of these large cities? All but three are near coastlines. Are any close to rivers or lakes? To find out, return to Construct mode and add the "U.S. Rivers" and "U.S. Lakes" datasets to the Layer List (you should add them below the U.S. Cities layer so they don't cover the cities). Next, return to Visualize mode to continue investigating.
To see the lakes, choose a Fill Color by "Name". Now, notice that two interior cities (Chicago and Detroit) are near rivers and lakes. Notice that all but one of these large cities are near some sort of major waterway. Can you find the one large city that is near neither a coast, nor river, nor lake?
Next, try creating selections for cities with populations of 500,000 or larger. Try the same for cities with populations of 250,000. As you do this, My World adds selections to the Layer Control Panel. You can click back and forth to see the different selections, as shown below in Figure18.
Figure 18. Changing selections within a layer
As you explore cities of different sizes, does the pattern hold? Are there exceptions?
You can continue exploring this data on your own. For example, try adding U.S. Highways to your map and seeing how this data relates to urban populations.
To learn how to save your work see the the My World tutorial on "How to Save your Work." You can find this and other useful tutorials by clicking on the Windows menu and selecting the Welcome Window, as show in Figure19 below.
Figure 19. Reopening the Welcome Window
The Welcome Window, shown in Figure20 below, contains links to a variety of useful resources to help you use My World.
Figure 20. Using the Welcome Window to access My World resources